The present invention relates to an auxiliary towing device attached to a tractor truck for towing another tractor truck, and more particularly to such devices equipped with hydraulic lifting components.
It is not uncommon for one hundred or more manufactured building modules to be employed in a single apartment, motel, office, or residential complex. Typically, such modules are transported from the factory to the construction site on relatively low slung highway semitrailers, such as those disclosed in U.S. Pat. No. 4,640,528. At a maximum, such highway semitrailers can accomodate two prefabricated building modules, so quite a few semitrailers and tractor trucks are needed to transport all of the modules to the site.
Advantageously, the low slung highway semitrailers, once emptied, may be stacked upon one another in groups of three and returned to the factory by a single tractor truck. Since the two remaining trucks have nothing to transport, a mechanism was sought whereby one of the tractor trucks could haul the other. In this manner, one out of every three drivers who carried building modules from the factory to the site could rest and relieve the other drivers on the return trip. In addition, fuel consumption and operating hours on the truck fleet could be reduced, since the engine on the truck being towed would not be running.
In the past, tractor trucks have been transported along the highways either in piggyback fashion by elevating the front end of one truck and attaching it by suitable connectors to the fifth wheel device of another, or in tandem fashion by elevating and connecting a front or rear end of one truck to the rear end of another. Towing a truck in piggyback fashion requires a substantial amount of conformity in the design of the towing and towed trucks, as well as an external lifting device to elevate the front end of the towed truck. Further, the rear axle or axles of the truck being towed in piggyback or tandem fashion must be removed to prevent damage to the differential and/or transmission.
Thus, an early attempt was made to devise a mechanism for lifting the rear end of a truck and towing it in back to back relation to the truck doing the towing. The early towing assembly included a support structure rigidly secured to and depending from rear portions of both the towing and towed trucks. Hydraulically actuated lifts were mounted on the support structures. A U-shaped tow bar was stowed on each truck, and sockets were provided in the support structure into which the free ends of the tow bar were inserted on the truck to be towed. Some of the problems with this system were the tendency for the tow bar to be forgotten or misplaced or for it to be difficult to manipulate due to its substantial weight and size. Another problem was the tendency for the lift to be damaged due to the very limited clearance between an upper portion of the hydraulic lift and front portions of the semitrailers during attachment and detachment with the tractor truck. The previous design also required special parts and a substantial amount of alteration to the existing truck frame.
Accordingly, the inventors were faced with the problem of devising a truck towing apparatus which could be used on both the truck doing the towing and the truck being towed without requiring the operator to stow and manipulate large, heavy frame members. In addition, the inventors sought to devise a towing apparatus that would lift the truck being towed higher and yet have a sufficiently low profile to avoid being struck when a semitrailer was being connected or disconnected with the tractor truck. Further, the inventors were confronted with the problem of designing a towing apparatus that did not require substantial alteration of the tractor truck to which it would be attached, as well as one that did not require expensive, special-order parts.